In the related art, as imaging devices used in cameras, imaging devices employing a rolling shutter system are known in which exposure is sequentially started for each horizontal line (hereinafter, referred to as a “line”), and a frame is generated by sequentially reading out video signals for each line. In the imaging device employing the rolling shutter system, an exposure period differs for each line. Accordingly, in a case where a flash or the like is on during a period shorter than a frame rate at which the imaging device reads out a video signal, there is a case where a band-shaped difference (flash band) in the luminance level is generated in a video displayed in accordance with a video signal within a read-out frame. Hereinafter, the luminance level is abbreviated to “level”, and a flash band is abbreviated to “FB”.
FIGS. 15A and 15B are schematic diagrams illustrating an example of an FB that is generated in a frame in the related art.
In FIG. 15A, the vertical axis represents the number of lines in the vertical direction, the horizontal axis represents the time (seconds), and the relationship between consecutive frames and a flash is illustrated.
An imaging device reads out video signals in the order from the side on which the number of lines in the vertical direction is small (in this example, a direction from the upper portion of a frame to the lower portion) and outputs the video signals. Over the first frame to the second frame, the flash is on.
FIG. 15B illustrates an example of videos for each frame.
When the flash is on from the first frame to the second frame, the flash has no effect on upper lines of the first frame that have already been read out, but a difference in the level is generated in lower lines of the first frame due to the effect of the flash. In the second frame, video signals of upper lines of the second frame are read out before a video signal of the lower-most line of the first frame is read out. Accordingly, a difference in the level is generated due to the effect of the flash in the upper lines of the second frame, but the flash has no effect on the lower lines of the second frame. As above, when the FB is generated in a frame, a lower portion of a video is brightened in the first frame, and an upper portion of a video is brightened in the second frame. Since the FBs are generated over a plurality of frames and the FBs are seen when a video is reproduced or a still screen is captured, the quality of the video may deteriorate.
In the related art, in order to suppress the effect of a frame in which an FB is generated on a video, a countermeasure such as correction of the frame for removing the difference in the level or discarding the frame is taken. As a premise of such a countermeasure, a method of detecting whether or not there is an FB has been reviewed.
In JP-A-2010-135921, as a method of detecting the FB, a method using a first condition that the presence of an area, in which the level of a pixel increases in the lower portion of a first frame and the upper portion of a second frame as a typical feature of the FB, is detected is disclosed. In this method, a decrease in the level of an area, of which the level increases in the first frame, in the second frame is set as a second condition. By adding the second condition to the first condition, incorrect detection of the generation of the FB in a case where the first condition is satisfied due to only the composition of a subject can be prevented.
In addition, as another method, in JP-A-2007-306225, a method is disclosed in which a frame, in which the exposure is saturated, is detected from among a group of consecutive frames acquired through imaging under appropriate exposure.